1. Field of the Invention
This invention generally relates to circuit boards, and more particularly, to a circuit board with embedded resistors and a method of fabricating the same.
2. Background of the Invention
The market for communication devices is growing at an amazing pace. Nowadays, the basic requirements for communication devices are small, thin and lightweight. With increasingly stricter communication standards, packing circuit components in a small device while retaining its efficiency becomes a major issue for circuit design. In recent years, system-in-package technology is developed to pack circuit components in multilayer printed circuit boards with a high density to meet market demand. Integration of passive discrete components, such as resistors, capacitors and inductors, into printed circuit boards may miniaturize the system packages as well as reduce assembly time and manufacturing cost.
One major concern for embedded resistor technology is control of resistance values because it may affect the yield of manufacturing process. Indeed, resistance values depend on the thickness of resistors after board lamination process, and thus, it is desirable to improve board lamination process for better control of resistance value. In addition, it is also desirable to develop a method to adjust resistance values of embedded resistors after completion of the lamination process to meet various needs.
U.S. Pat. No. 4,443,782 describes a method for regulating the resistance value of a thick film resistor by adjusting the length of a slot located in the resistive material region. Variation of the resistance value is a linear function of the slot length. A slot may be formed by use of a grinding machine or a laser beam. U.S. Pat. No. 4,899,126 describes thick film resistor type printed circuit board having a common terminal electrode for connecting multiple resistors. The patent also mentions using laser beam to form slots to adjust resistance value. Both methods described above are for surface-mounted resistors and do not apply to embedded resistors.